Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$135.31	6.348%	$143.8995	$143.90	$143.90	$143.90
Purchase #2	$128.56	8.731%	$139.7846	$139.78	$139.80	$139.80
Purchase #3	$10.91	12.543%	$12.2784	$12.28	$12.30	$12.30
Purchase #4	$24.83	12.344%	$27.895	$27.90	$27.90	$27.90
Purchase #5	$18.60	3.720%	$19.2919	$19.29	$19.30	$19.30
Purchase #6	$205.27	8.855%	$223.4467	$223.45	$223.45	$223.40
Purchase #7	$89.54	5.509%	$94.4728	$94.47	$94.45	$94.50
7 purchase totals =	$613.02		$661.0689	$661.07	$661.10	$661.10